The present invention relates to the biofouling of various systems containing aqueous solutions and more particularly relates to monitors to detect or record biofouling and methods of monitoring or detecting biofouling.
Biological fouling on surfaces is a serious economic problem in many commercial and industrial aqueous process and water handling systems. The fouling is caused by a biomass which is the buildup of microorganisms and/or extracellular substances and by dirt or debris that become trapped in the biomass. Bacteria, fungi, yeasts, diatoms and protozoa are only some of the organisms which cause buildup of a biomass. If not controlled, the biofouling caused by these organisms can interfere with process operations, lower the efficiency of processes, waste energy, and reduce product quality.
Cooling water systems used in power-generating plants, refineries, chemical plants, air conditioning systems and other commercial and industrial operations frequently encounter biofilm problems. Biofilm is the buildup of layers of organisms. Cooling water systems are commonly contaminated with airborne organisms entrained by air/water contact in cooling towers as well as waterborne organisms from the systems makeup water supply. The water in such systems is generally an excellent growth medium for these organisms. If not controlled, the biofilm biofouling resulting from such growth can plug towers, block pipelines, and coat heat transfer surfaces with layers of slime, and thereby prevent proper operation and reduce equipment efficiency.
Industrial processes subject to problems with biofouling include those used for the manufacture of pulp, paper, paperboard, and textiles, particularly water laid nonwoven fabrics. For example, paper machines handle very large volumes of water in recirculating systems called "white water systems". The white water contains a pulp dispersion. The furnish to a paper machine typically contains only about 0.5% of fibrous and non fibrous paper making solids, which means that for each ton of paper, almost 200 tons of water pass through the paper machine, most of it being recirculated in the white water system.
These water systems provide an excellent growth medium for microorganisms, which can result in the formation of microbial slime in headboxes, water lines, and papermaking equipment. Such slime masses not only can interfere with water and stock flows, but when they break loose, can cause spots or holes in the paper as well as web breaks that cause costly disruptions in paper machine operations.
The control of microbial activity has traditionally been the province of toxic chemicals. U.S. Pat. Nos. 3,959,328, 4,054,542, and 4,285,765 are illustrative of the methods that rely on killing the offending microorganisms with toxic chemicals. Such method shave received the majority of the research effort because of the logic of eliminating the problem by eliminating the offending organism and because of the large number of available organic and inorganic chemicals that will kill microorganisms.
Several attempts to control the negative effects of biological activity either avoid the use of toxic chemicals or mitigate their use or impact on the environment. For instance, U.S. Pat. Nos. 3,773,623 and 3,824,184, both to Hatcher et al., relate to the use of the enzyme levan hydrolase to control the formation of bacterial slime in industrial water systems.
While efforts are continually made to control or prevent biofouling, the water systems, and especially the industrial water systems, still need to be shut down for cleaning or removal of the biofouling that has built up and which was not prevented by the introduction of biofouling control compositions. Although the introduction of microbicidal or anti-fouling compositions reduces the number of times a system has to be shut down for cleaning, it would be beneficial to have a biofouling monitoring system which enables the users to determine when biofouling has reached levels which require a shut down and cleaning. Otherwise, if users of the water systems are not aware of the biofouling buildup, such biofouling can result in poor quality products being made such as paper having spots or holes or could even be more detrimental such as a clogging of various lines used to supply feedstock to the water system. Thus, it is most preferred to have an early warning system which informs the users of the water systems of a potentially biofouling situation which needs correction either by the introduction of more chemicals or a shut down. If the users of the water systems know in advance that a shutdown is necessary, then plans can be made ahead of time to finish, for instance, a paper run or to increase the amount of chemicals in the water system to avoid poor quality products or damage to equipment in the water systems.